E0001 Computers in Engineering Built in Functions.

E0001 Computers in Engineering

Built in Functions

General Notes

Error in Assignment A-E & M-R - TYPO Volume should be 152.13, 22.44, 5.77

Assignment S-Z constant = 2.749*10-8

Assignment 2 due 9 April but …. submit until 12 April

Ass1 and 2 handed back after holidays..

Readings and Exercises

Schneider Section 3.4 p 72-78Schneider Practice Problems 3.4 p

78; programming problems #’s 57, 60, 62, 66, 68

Rem statements

Rem short for REMARKused for adding comments to codeuseful for the programmer, not the

usernon executable lineTwo ways of adding comments

REM ‘

Examples

REM this line is a commentREM This program will calculate….REM This program was written by….

INPUT r,b,h ‘radius, base, height

READ n$, no$ ‘name, number

Numeric Functions

covers common numeric and trigonometric terms square root - SQR(x) SIN(angle), COS(angle), TAN(angle)

BEWARE - (angle) must be in RADIANS

LOG (x)see handout for more examples

Examples of Numeric Functions

SQR (x) - square root of x where x is variable - given a value by the program

or the user arithmetic operation - (6-4)/360*12

ABS - absolute value ABS(-3) = 3; ABS(7) = 7 ABS(SQR(CINT(x)))

String Functions

allows examining strings or parts; combining strings

allows string comparisons using <, >, = (relational operators)

Examples of String Functions

LEN(s) - s is known as the argument returns the length of the argument i.e.

the number of characters contained in the argument

blanks are counted as characters LEN(“John and Mary”) = 13 Z$ = “John and Mary”: LEN(Z$) = 13 IF LEN(Z$) = 20 THEN PRINT “HELLO”

LEFT$(x$, n) - x$ is any string; n is an integer from 0 to LEN(x$) x$ = “John and Mary” PRINT LEFT$(x$,4) - gives the output John

see also MID$(x$,n,m) and RIGHT$(x$,n)

LCASE$(X$); UCASE$(X$); INSTR(n,X$,Y$)

VAL(X$) - converts a string whose contents represent a number to its numerical form. ignores leading blanks converts a string up to its first nonnumerical

character into its numerical value.

Built-in Functions

prewritten “subroutine” that does one operation

returns ONE value onlyimplimented by arithametic statement

variable = equationdesigned to manipulate both numerical

and string datacover common calculations

Computers in Engineering

PRINT USING STATEMENT

Overview

In a circuit three currents are represented by the variables cur1, cur2, cur3

Plan and write a program to input these values and calculate and display the average current

Plan

Outputs…Inputs….Process…flowchart/plan/pseudocode

INPUT statements

Write input statements to enter these variables

INPUT “current 1”, cur1INPUT “current 2”, cur2INPUT “current 3”, cur3

In Memory

User enters 9.16, 12.4, 0.9cur1 9.16cur2 12.4cur3 0.9

Calculate total and average currents and print

totCur = cur1 + cur2 + cur3AvgCur = totCur / 3PRINT , cur1PRINT , cur2PRINT , cur3PRINT , “________”PRINT , TotCurPRINT “Average”, AvgCur

Qbasic Screen

To add units to a variable

PRINT “Current”; cur1; “amps”PRINT “prompt” ; variable list ;

“prompt”

PRINT USING

PRINT USING statement can be used instead of PRINT to make decimal points line up

has general form -PRINT USING “format string”;expression

liste.gPRINT USING “ ##.##”; cur1

Format string

String of characters letters, numbers, punctuation

some have special meanings if no special meaning qb will simply

display it on the screen if has special meaning qb uses it to

determine the format for displaying one of the expressions in the list

Character Meaning

# A digit position in the format for anumerical output

. (period) The decimal point position in theformat for a numerical output

^^^^ or ^^^^^ Specifies scientific format for thenumerical output

\spaces\ Characters format the beginningof the value of a string variable:2 + the number of spacecharacters will be printed

& The value of a string variable

Formatting numbers

# # #.# # displays 3 digits preceding the decimal

fewer than 3 before qbasic leaves a spacemore than 3 - will be displayed correctly but

in a different format, will also precede it with a % character

displays 2 digits after the decimalfewer than 2 - displays zeros for the missing

digitsmore than 2 - displays the rounded value

Format string

Fmt$ = “current is ##.## at ###.# volts”

PRINT USING Fmt$; cur; voltsc.f.PRINT USING “format

string”;expression list

Scientific notation - e.g. 2E-6^^^^

represent positions for E, minus or plus sign, two digit exponent

^^^^^ for double precision numbers represent positions for E, minus or plus

sign, three digit exponente.g.FMT$ = “current is ##.###^^^^ at ##.#### ^^^^

volts”

Output? Current is 23.5, volts are 117.6

FMT$ = “current is ##.###^^^^ at ##.####^^^^ volts”

Current is 2.350E+01 at 1.1760E+02 voltsadditional strings can be added

FMT$ = “current is & ##.###^^^^ at ##.####^^^^ volts”

curType$ = “direct”

PRINT USING Fmt$; curType$; cur; volts

Current is direct 2.350E+01 at 1.176E+02 volts

Take a break

Return for assignments

Write a program to convert a US customary system length in miles, yards, feet and inches to a Metric System length in kilometres, meters and centimetres. After the number of miles, yards, feet and inches are requested as input, the length should be converted entirely to inches and then divided by 39.37 to obtain the value in meters. The INT function should be used to break the total number of meters into a whole number of kilometres and meters. The number of centimetres should be displayed to one decimal place. Some of the needed formulas are:

Total inches = 63360 * miles + 36 * yards + 12 * feet + inches

Total meters = total inches / 39.37 Kilometres = INT (meters/1000)

Kepler's Third Law states that for objects with an elliptical orbit (such as satellites orbiting Earth or planets orbiting the sun), the square of the Period is proportional to a3, where a is half the length of the major axis of the ellipse. For nearly circular satellite orbit above Earth, a can be approximated by the radius of the earth plus the altitude of the satellite. Thus

a ~ 6378 kilometers + altitude

If the Period is expressed in minutes and the length of the major axis is expressed in kilometers, then

Period 2 = 2.749E-8*10-4*a3

Write a program to produce the table shown below. The information in the first two columns should be stored in DATA statements and the period should be computed and displayed to an appropriate number of decimal places.

Type of Satellite Altitude (km) Period (minutes)

Earth imaging 400

Low-altitude communications 1500

Geosynchronous communication 35789

The general law of perfect gases states that PV / T = n R = constant

where • P is the gas pressure (in atmospheres),

• V is the volume (in litres),

• T is the temperature (in degrees Kelvin),

• n is the number of moles,

• R is the constant of perfect gases (0.82 Liter-atm/Kelvin-mole).

Write a program to produce the table for the case n=1 thus giving V = RT/P. The user with an INPUT statement should enter a temperature (in Celsius) and pressure. Two new temperatures (in Celsius) should be calculated from the original, one increased by 500 and one decreased by 500. A corresponding pressure for each new temperature should be entered by the use of an INPUT statement. The temperature in Kelvin and the Volume should be calculated for the three temperatures and displayed. A sample output is shown below:

TemperaturePressure TemperatureVolume

(Celsius) (atm) (Kelvin)(liter)

150 2.280 423 152.13200 17.287 473 22.44250 74.375 523 5.77

The period P of a pendulum of length L and maximum displacement angle is given by the formula

P =

write a program that requests as input the length and maximum angle of displacement, and displays the period of the pendulum

Problem

L/ g(11

4sin (

2))2

Tutorial

1. What will be the contents of x after the following statement is executed?

LET x = SQR((9 + 7) / ( 4 * 2) + 2)

2. Suppose num = 123.4567. What is the output?

LET num = INT(100 * num + .5) / 100

PRINT num

3. What output is generated by the following statements (show the output EXACTLY as it would appear on the screen)? PRINT SQR (3^2 + 4^2) PRINT MID$ ("Milkshake", 5, 5) PRINT UCASE$ ("123jump")

5shake123JUMP

try this for yourself

4. The following statements are valid. (T/F)

LET H$ = "Hello"

LET a$ = INSTR(H$, 3)

5. Given the data in the variable y$ shown below, which of the following statements will assign the value ALL to x$?

LET y$ = "WHEN ALL ELSE FAILS, READ THE DIRECTIONS"

(a) LET x$ = MID$(y$, 6, 3)

(b) LET x$ = INSTR(6, y$, "ALL")

(c) LET x$ = LEFT$(y$, 3)

(d) LET x$ = MIDDLE$(y$, 6, 3)

(e) LET x$ = RIGHT$(y$, 8)

6. What will be displayed when the following program is executed?

LET a$ = "THE WHOLE"

LET b$ = "PART"

LET c$ = MID$(a$, SQR(4), LEN(b$))

PRINT c$

END

The End